Intermediate Floor Psi Value Calculator (E6)

E6 SAP / Approved Document L reference junction

Schematic cross-section of the intermediate floor (E6) showing the structure, insulation line and the heat-bridge path — Schematic of the intermediate floor (E6) — not to scale. Model your actual build-up in ΨMonkey.

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What the intermediate floor is

The intermediate floor junction is where an upper floor inside the dwelling meets the external wall — the floor structure (joists or slab) bears into or against the wall.

Why it matters

The floor structure can interrupt the wall insulation where it meets or penetrates it, giving heat a path out at every floor level around the perimeter.

How to model it

Paint the wall build-up and the floor deck meeting it, keeping the wall insulation continuous past the floor zone, then solve.

Where the wall insulation runs unbroken past the floor, the Ψ-value is low; problems arise when the floor breaks the insulation line.

Related build-ups: the U-values either side of this junction

The Ψ-value at the intermediate floor depends on the walls, floors and roof around it — so the first step is knowing the U-values of those elements. Typical figures for the build-ups that pair with this junction:

Model your exact build-up and read its U-value with the free U-Monkey calculator (PDFs included free), then come back here and solve the junction in ΨMonkey.

Free to model — no subscription

ΨMonkey isn't a monthly licence or a per-seat subscription. Build the intermediate floor on the grid, solve it, and read the Ψ-value and f_Rsi on screen for nothing. You only pay £25 +VAT (£30 inc VAT), once, when you need the Building Control-ready PDF for that junction — so calculating a single detail never means signing up to anything. Calculated psi values are often the cheapest route to a SAP 10 pass, so the maths can pay for itself.

Frequently asked questions

What is the intermediate floor (E6)?

The intermediate floor junction is where an upper floor inside the dwelling meets the external wall — the floor structure (joists or slab) bears into or against the wall. The floor structure can interrupt the wall insulation where it meets or penetrates it, giving heat a path out at every floor level around the perimeter.

How do I calculate the intermediate floor psi value?

Paint the wall build-up and the floor deck meeting it, keeping the wall insulation continuous past the floor zone, then solve. ΨMonkey solves it to BS EN ISO 10211 and returns the Ψ-value (W/m·K) and the f_Rsi temperature factor on screen, free.

Is it free, and is there a subscription?

No subscription and no licence — modelling the junction and reading off the Ψ-value is free in your browser. You only pay £25 +VAT (£30 inc VAT) when you export the Building Control-ready PDF for that junction.

Can I use the result in a SAP or HEM assessment?

Yes — a calculated Ψ-value to ISO 10211 can replace the SAP default for this junction, and Where the wall insulation runs unbroken past the floor, the Ψ-value is low; problems arise when the floor breaks the insulation line.

Other junctions

ΨMonkey models any junction. Jump to another common one:

Intermediate Floor Psi Value Calculator